Instability Mechanism of a Rotating Disc Subjected to Various Transverse Interactive Forces

In the past three decades, numerous papers have bee n publishedon the dynamics of rotating discs. most of them have focused on the ma thematical modeling and solution for a specific interactive force, such as a n elastic force produced by a stationary spring or a damping force from a statio nary viscous damper. Few of them have looked into the instability mechanisms. This study has established a generalized approach to investigate the instability mechanisms that are involved in the interaction between a rotating and an arbit rary interactive force. An energy flux equation has been developed, which leads to the following conclusions: (1) The possibility of the occurrence of instability due to any interactive forc es may be identified based on the energy flux analysis, even without solving equ ations. (2) Instabilities will occur if the interactive forces are in phase with the vel ocity measured at the interactive point from the coordinates rotating with the d isc. (3) Instability cannot occur when a rotating disc is subjected to a stationary c onstant lateral force, but a stationary harmonic lateral force, a moving constan t lateral force or a moving harmonic lateral force may cause instability. (4) Conservative forces may only cause coupling instability associated with two modes, and non-conservative forces usually cause terminal instability where onl y one mode is involved.

Analgesic effects and hemodynamic mechanisms of perpendicular and transverse needling at Sanyinjiao(SP 6) in patients with primary dysmenorrhea: A randomized controlled trial

Objective: To explore the analgesic effects and uterine hemodynamics of perpendicular needling(PN)and transverse needling(TN) at SP 6 in patients with primary dysmenorrhea(PD).Methods: In this randomized controlled trial, patients with PD diagnosed with cold-dampness congealing pattern were randomly assigned in a ratio of 1:1 to receive PN or TN at bilateral SP 6 for 10 min.Acupuncture was performed when the menstrual pain score was over 40 mm on the first day of menstruation, as measured using the visual analog scale for pain(VAS-P). The primary outcome was average menstrual pain(VAS-P). Secondary outcomes included the pulsatility index(PI), resistance index(RI), and systolic-diastolic peaks ratio(S/D) in uterine arteries as measured using color Doppler ultrasonography;anxiety as assessed using the Hamilton Anxiety Rating Scale(HAMA), blood pressure(BP),and heart rate(HR).Results: Forty-eight patients completed the study. The TN group exhibited a significant reduction in VAS-P scores(-5.71 mm, 95% confidence interval(CI): -8.78, -2.63, P =.001), RI values(-0.05, 95% CI:-0.09, -0.01, P=.015), and HAMA values(-2.50, 95% CI: -4.78, -0.22, P=.032) when compared with the PN group. No significant differences in PI, S/D, BP, or HR values were observed between the two groups(P >.05).Conclusion: TN at SP 6 was superior to PN in alleviating menstrual pain and anxiety in patients with PD.This analgesic effect of TN may be due to its better ability to improve uterine arterial blood flow via decreases in RI values.

Characteristics of an Accelerated Transverse Mechanical Pulse and Its Implications

In this report, two nontraditional mechanical wave-related issues are addressed. 1) Customary, for practical reasons the characteristics of the sinusoidal pulses progressing at a constant speed only is considered. And 2) the literature search shows that there has been no interest in exploring the characteristics of the pulses in a curvilinear two-dimensional space. By relaxing the first restriction we consider a scenario that which a mechanical pulse progresses with variable speed, specifically at a constant acceleration. We develop its equation of motion conducive to a homogenous linear partial differential equation with variable coefficients then we apply it to a practical problem. To address the 2nd point we depict a circular orbital embodying two Gaussian pulses circulating in opposite directions. Utilizing a Computer Algebra System (CAS), Mathematica, we develop animations visually easing the comprehension of the issues on hand.

Deformation analysis of transversely isotropic coal-rock mass with porous and cracks

Coal-rock as a typical sedimentary rock has obvious stratification,namely it has transversely isotropic feature.Meanwhile,deformation leads to coal-rock mass having the characteristics of different porous and crack structures as well as local anisotropy.Equivalent axial and circumferential strain' formulas of the pure coal-rock mass specimen with a single crack were derived through the establishment of equivalent mechanical model of standard cylindrical coal-rock specimen,and have been widely used to a variety of media combined different structures containing multiple cracks.The complete stress strain curve of a real coal-rock specimen was obtained by the CTC test.Additionally,according to the comparison with the theoretical value,the theoretical mechanical model could well explain the deformation characteristics of coal-rock mass and verify its validity.Further,following features were analyzed:strain normalized coefficient and elastic modulus(Poisson's ratio) in vertical and parallel direction to the stratification,stratification angle,porosity,pore radius,normal and tangential stiffness of crack,and the relationship of different crack width with different tangential stiffness of crack.Through the analysis above,it substantiate this claim that the theoretical model with better reliability reflects the transversely isotropic nature of the coal-rock and the local anisotropy caused by the porous and cracks.

Strain Effect of Manganin Transverse Piezoresistive Gauge and Measurement of Dynamic Transverse Stresses

Manganin piezoresistive gauges have been extensively used in dynamic stress measurement for decades.It is noted,however,that when used to measure transverse stresses,considerable strain effect is caused as the consequence of change of electrical resistance resulted from bending of wires in the longitudinal-strain-experiencing sensing element of the gauge,a phenomenon discussed in this paper theoretically as well as experimentally.This effect yields unwanted signals to blend with output piezoresistive signals and is not negligible,hence decreases measurement accuracy sizably if not properly handled.To overcome this drawback,a new type of manganin transverse piezoresistive gauge has been developed by authors of this paper,which can reduce the resistance increment to acceptable low level so as to effectively bring the adverse effect under control.

High Permeability of Boron along the Transverse Direction of Wood under High-Voltage Electrostatic Field (HVEF) Treatment

Permeability of wood preservative is one of the most significant factors for protection of wood construction.Ani-sotropic flow permeability was involved in different directions of wood with higher flow resistance in the trans-verse and lower longitudinal directions.In this study,boron acid solution was brushed onto the tangential section of air-dried wood cubes and boron penetration along wood transverse direction was investigated under free dif-fusion,vacuum and HVEF treatments.Multi-scale boron distribution,FTIR measurement,leaching property,mechanical properties and fungistatic characteristic were investigated for free diffusion,vacuum and HVEF trea-ted samples respectively.The results revealed that boron exhibited high permeability along the transverse direc-tion with the penetration depth of≈35 mm for HVEF treated samples and≈1 mm for free diffusion and vacuum treated samples.For HVEF treated samples,no significant decrease of hardness,compression modulus of elasti-city and strength were found in the treated samples.Better fungistatic characteristic was showcased in HVEF trea-ted samples exposed to white rot fungi.Thus,HVEF treatment has a positive effect on boron permeability and the improvement of penetration depth of preservatives hence playing a significant role in wood protection and prolonging the service life of wood construction.

Interaction between transverse isotropy rock slope and supporting structure

In order to study the interaction between transverse isotropy rock mass and supporting structure,the laboratory tests for rock sampled from the slope at expressway project were carried out,and the parameters of elasticity for transverse isotropic rock were determined by the uniaxial compression tests for rock sample with different strike of stratification plane.Then,based on the relationship of stress-stain for transverse isotropic rock mass,the analytical model was established for the interaction between transverse isotropic rock mass and frame beam with pre-stressed anchor cable.Furthermore,the conception of the best anchorage-angle in pre-stressed anchor cable was proposed.At last,the parameters of the interaction between transverse isotropy rock mass and frame beam with pre-stressed anchor cable were investigated by finite element method,and the best anchorage-angle in pre-stressed anchor cable was obtained.The rules of the influence of the directivity of stratification plane on supporting structure were determined.The results show that the analytical model and numerical method on the design of pre-stressed anchor cable with frame beam supporting for transverse isotropy rock slope are reasonable and reliable in practical engineering design.

Multiscale Failure Mechanism Analysis of SiC Fiber‑Reinforced TC17 Composite Subjected to Transverse Tensile Loading at Elevated Temperature

This study presents a multiscale method to evaluate the transverse tensile strength and failure mechanism of SiC_(f)/TC17 cruciform specimen machined from a large-size ring.The mechanical properties and failure of the specimen were evaluated through a macroscale model under transverse tensile loading at 200°C.A mesoscale model was developed to analyze the transverse tensile behavior and failure of the composite specimen.Interfacial debonding,plastic deformation of matrix and cladding,and damage to the composite core were incorporated into the mesoscopic and macroscopic models.The stress–strain curves and fracture modes obtained from the numerical simulation showed good agreement with the experimental curves,acoustic emission test results,and fracture morphology.The simulation results suggested that the damage to the central region interface and the plastic deformation of the matrix initiated first and propagated outwards.Subsequently,the interfacial failure,matrix failure,and formation of macro-crack developed,which led to the crack of the titanium matrix composite core.Finally,cladding was plastically deformed and crack developed,which led to the severe failure of the cruciform specimen.

Understanding the superior mechanical properties of Mg-3Al-Zn alloy sheets:Role of multi-type unique textures

Mg-3Al-1Zn(AZ31)sheets were produced by transverse gradient extrusion(TGE)process.The flow behavior and dynamic recrystallization during extrusion were systematically analyzed.The microstructures,textures,and mechanical behavior of extruded AZ31 sheet were also analyzed and compared with conventional extruded(CE)sheet.The results showed that fine grain structure and multi-type unique textures were formed in TGE sheet because of the generation of extra flow velocity along transverse direction(TD)and flow velocity gradient along extrusion direction(ED)during extrusion.The basal poles gradually deviated away normal direction(ND)from edge to center of the TGE sheet along TD,and the largest inclination angle at center region reached around 65°.Furthermore,the basal poles inclined from ED to TD 40°-63°,except for the center region of TGE sheet.The TGE sheet presented higher ductility and strain hardening exponent(n-value),but lower yield strength and Lankford value(r-value)in comparison with the CE sheet.Both the basal<a>slip and tensile twins were easy to be activated during deformation,and the largest elongation of 41%and the lowest yield strength of 86.5 MPa were obtained for the ED-center sample in the TGE sheet.

溶蚀作用下层状灰岩力学模型研究

【目的】层状灰岩的不同层面会表现出不同的力学特性,为了研究溶蚀作用下不同层面倾角的层状灰岩力学特性影响规律,确立溶蚀作用下横观各向同性应变软化模型对溶蚀作用下层状灰岩力学特性进行描述。【方法】首先,采用横观各向同性应变软化模型来描述无溶蚀作用下层状灰岩平行和垂直层面的力学特性,并结合对0°、30°、60°和90°四个层面倾角的层状灰岩单轴压缩试验结果的整理分析,得到无溶蚀作用下平行和垂直层面的层状灰岩核心参数,即弹性模量、黏聚力和内摩擦角等;然后,基于溶蚀作用下层状灰岩力学发生改变机制分析,确定溶蚀作用下层状灰岩的塑性力学模型;最后,结合溶蚀作用下层状灰岩单轴压缩力学试验结果,采用FLAC—强度折减法联合求解确定溶蚀作用下层状灰岩力学模型中力学参数(弹性模量、黏聚力)随溶蚀作用的变化规律。【结果】结果显示,溶蚀等效时间和卸载应变(裂纹发育程度处卸载应变)对不同层面倾角层状灰岩力学特性影响不同,溶蚀等效时间对层面倾角为0°的层状灰岩参数影响最大,卸载应变对层面倾角30°时的层状灰岩参数影响最大。表现为溶蚀等效时间对基质黏聚力c2的影响大于层面黏聚力c1,卸载应变对c1影响大于对c2的影响。【结论】结果表明,横观各向同性应变软化模型能较准确地获取层状灰岩不同层面倾角力学强度参数与溶蚀作用之间的变化关系式,较好地表征溶蚀作用下不同层面倾角层状灰岩力学特性,可为岩溶地下洞室围岩稳定性分析提供理论基础。

碳纤维增强热塑性树脂基复合材料界面性能研究

采用宏观力学性能测试(0°压缩测试、90°拉伸测试、层间剪切测试、弯曲测试)、微观力学性能测试(微脱粘测试)、扫描电镜(SEM)以及偏光显微镜观察,对不同碳纤维/热塑性树脂复合材料界面性能进行了多维度的研究。

一种游动傅科机械编排的捷联惯性间接极区导航算法

针对指北方位、游移方位等机械编排的惯性导航系统在极区附近出现计算溢出、导航误差发散、方向基准缺失等问题,本文提出了一种基于游动傅科机械力学编排的捷联惯性间接极区导航算法。首先,推导了传统坐标系和横向坐标系下的游动傅科机械编排位置、速度和姿态转换关系,并设计了完整的捷联惯性极区导航流程。其次,在详细分析载体沿经线穿越极点时的导航解算性能基础上,提出了一种游动傅科机械编排的捷联惯性间接极区导航算法。实验结果表明,该算法能够实现传统导航与横向导航方式的平滑切换,并借助横向导航信息解决载体穿越极点时无法导航的难题。

利用单边核磁共振研究樟子松木材干燥水分迁移规律

研究木材干燥过程中水分迁移可以更高效的利用木材.利用单边核磁共振技术(single-sided NMR)可沿木材不同方向进行一维测量的优势来探究木材在干燥过程中水分沿着轴向和弦向传递过程中不同测量深度的变化规律.本文以樟子松木材为研究对象,对其进行封胶处理使水分只沿着轴向或弦向传递,利用表观横向弛豫时间(T2app)来探究其在干燥过程中不同测量深度位置处的含水率变化.结果表明:樟子松木材在干燥过程的前2 h其接近蒸发面处存在少部分自由水,之后在干燥过程中基本上不存在自由水,且靠近蒸发面存在明显的含水率梯度;水分沿轴向传递时越远离蒸发面,水分分布相对均匀,弦向传递时越远离蒸发面,每层水分差异越明显.单边核磁共振技术可以检测木材不同测量深度位置的含水率,可为研究水分在木材中的迁移机理提供理论依据.

横坡段桥梁双桩双柱式结构受力特征与解析模型

山区桥梁基础不可避免地建立在陡坡上,不稳定斜坡变形或破坏将会对上覆桥跨结构安全造成严重威胁,亟需研究高效、可靠的力学模型。首先,对横坡段桥梁双桩双柱式结构划分不同特征段,分析其受力特性;其次,考虑桩土相互作用和桩顶变形协调关系并引入边界条件,建立适用于横坡段桥梁双桩双柱式结构内力及位移的简化模型;第三,综合考虑P-Δ效应及盖/系梁对桩柱受力影响,引入相邻特征段满足的连续条件(即位移、转角、剪力及弯矩连续),建立挠曲微分方程并以MATLAB为平台编制相应计算程序,提出横坡段桥梁双桩双柱式结构基础内力及位移的幂级数解;最后,将模型结果与有限元计算结果对比,验证模型的可靠性。研究结果表明:本文提出的模型将桥墩与桩基础视为整体,对于多道系梁的结构分析该模型同样适用;模型考虑了横向联系对两桩轴向力和弯矩的分配,可获取横向联系中的横向力;模型不需要假设自由段剪力和迭代计算。随着剩余下滑力增大,结构各特征段前后桩位移和弯矩明显增加;横向联系对桩基位移及内力进行了重新分配,有较强的约束作用,能够较好地改善前后桩受力与变形情况。

基于超声纵横波原位法的螺栓预紧力检测研究

针对超声纵横波的螺栓预紧力原位测量精度受几何层面和材料层面因素的影响,通过声弹力学的理论推导,提出了基于形状因子和材料因子的螺栓预紧力超声原位检测模型,并对多种规格、等级、厂商的螺栓的形状因子和材料因子的影响进行试验。结果表明,本测量方法具有较高的拟合度,且可将形状因子λ<0.3作为适用条件。由此得出,通过测量验证了理论推导的正确性,定量地获得了各种因素对测量精度的影响范围,为建立纵横波虚拟标定曲线算法和数据库提供了坚实的基础。

不同参数条件下双螺母螺栓连接松动过程的实验研究

针对工程中常见的双螺母螺栓连接,建立了螺栓上下螺母拧紧力矩与预紧力之间的关系,并验证了其正确性,通过横向振动实验得到了不同参数条件下双螺母螺栓连接剩余预紧力的百分比,分析了在横向载荷作用下振动幅值以及上下螺母拧紧力矩配比对双螺母螺栓连接松动的影响,给出了双螺母螺栓连接中上下螺母的最佳拧紧力矩配比,分析了双螺母螺栓连接螺纹磨损机理。

立交匝道小半径钢混组合连续梁桥受力特性分析

以立交小半径匝道桥为工程实例,建立有限元模型,对钢箱梁和混凝土桥面板受力分析。针对墩顶负弯矩区域提出双重组合、先铰接后固结和优化施工顺序3项改善措施。结果表明,各个施工阶段钢箱梁应力和混凝土桥面板横向受力均满足规范要求。采用双重组合和先铰接后固结技术可以降低钢箱梁底板压应力约27.7%和9.8%,优化施工顺序措施能使混凝土桥面板在短期荷载组合下保持受压状态。

预制T梁架设阶段横向温度梯度作用侧向变形研究

为控制大跨预制混凝土T梁架设阶段由横向温差导致的侧向失稳,以标准截面预制混凝土T梁为背景,对架设阶段横向温度梯度作用下的T梁侧向变形进行研究。建立截面热传递理论模型,通过热传递有限元分析得到主梁温度时程与分布,并与实测结果对比以验证有限元分析准确性,分析极端环境条件下(最高气温、最低气温、最大温差和最强太阳辐射)截面横向温度梯度分布,提出横向温度梯度多线性分布模式和预制混凝土T梁在横向温度梯度作用下的侧向变形简化分析方法。结果表明:热传递有限元分析计算结果与实测结果吻合;混凝土T梁顶、底板温差明显,且均产生较大的横向温度梯度;顶、底板及腹板的最高温度均出现在太阳直射边缘,最低温度出现在横向中心位置附近;采用简化分析方法计算预制混凝土T梁在横向温度梯度作用下的侧向变形,并得到不同标准截面梁在极端横向温度梯度下的侧向变形与跨径的关系,可为预制混凝土T梁架设时侧向变形控制提供参考。

Fabrication and Characterization of Tungsten Heavy Alloys Using Chemical Reduction and Mechanical Alloying Methods

A novel reduction technique has been developed to synthesize nano-sized tungsten heavy alloys powders and compared with the same powders processed by mechanical alloying technique. In the first method, nano-sized tungsten heavy alloys powders have been obtained by reduction of precursors obtained by spray drying of several appropriate aqueous solutions, which were made from salts containing tungsten, cobalt, and nickel. By adjusting the stoichiometry of the component of the solutions, it is possible to obtain the desired chemical composition of the tungsten heavy alloys powders. In the second method, highly pure elemental powders of tungsten heavy alloys have been mechanically alloyed in a tumbler ball mill for different milling time. The investigated tungsten heavy alloy powders with the composition (95%W-3.5%Ni-1.5%Fe), (93%W-4.5%Ni-1.0%Fe-1.5%Co), and (90%W-6%Ni-4%Cu) have been prepared using both methods. The prepared powders have been compacted at 70 bar (200 MPa) and sintered in vacuum furnace at 1400℃. Vacuum sintering was carried out to achieve full densification of the produced tungsten heavy alloys. The investigated materials were going to be evaluated the physical and mechanical properties of the sintered parts such as density;electrical conductivity, hardness, and transverse rupture strength. The results reveal that, the grain size of alloys fabricated by chemical reduction technique (53.1 - 63.8 nm) is smaller than that fabricated by mechanical alloying technique (56.4 - 71.4 nm).

超大跨斜拉桥横桥向恒载非对称力学行为

为研究横桥向非对称恒载对大跨度斜拉桥受力行为的影响,以常泰长江大桥为工程背景,对横桥向非对称恒载桥梁结构的力学行为进行分析,并提出了合理的控制措施以实现理想的成桥状态.提出了一种索力快速优化的方法,采用上下游索力不对称和降低铁路二期恒载的措施解决横桥向不对称恒载引起的主梁扭转、主塔偏位问题,实现了合理的成桥状态.结果表明:通过上下游索力不对称可以有效地控制主梁扭转,斜拉索顺桥向不平衡分力和横桥向不平衡分力产生的横桥向弯曲变形大小基本一致,方向相反,有利于降低主梁横桥向弯曲变形;通过减小横桥向不对称恒载的差值可以有效地控制主塔横桥向偏位.